The purpose of this research is the development of technology to make complex-shape closed-section parts directly from sheet blanks (direct sheet forming). Closed-section parts with large expansion of the circumferential length are expected to be formed by direct sheet forming. In this work, first, the deformation type of curved circular tubes is confirmed from the results of FEM analysis. Next, with reference to curved circular tubes, the deformation type of curved conical tubes is discussed. The validity of FEM analysis is confirmed by comparison with experimental results of curved circular tubes. It is clarified that curved circular tubes and curved conical tubes are formed with the same processes and deformation types (bending of sheet, axial bending of U-section, shrink flanging and plane-strain compression). However, in the 2nd process (axial bending of U-section) of forming curved conical tubes, longitudinal strain at the narrower side is greater than that at the wider side.
